Method of producing pressings to form permanent magnets



June 15, 1965 KARL-HEINZ BUTTNER ETAL ,1 7

METHOD OF PRODUCING PRESSINGS TO FORM PERMANENT MAGNETS Filed NOV. 15.1961 lllllll Fl .l

OOOOOOO OOOOOOO INYENTORS KARL- HEINZ BUTTNER HEINRICH v6LLER BY W 119%)Mm OOOOOOO ATTORNEYS United States Patent 3,189,667 METHGD 0F PRQDUCENGPRESSHNGS Ti) Flitlll /l PERMANENT MAGNETS Kerb-Heinz "jiittner,Dortmund, and Heinz Viiller, Dortmund-Berghoien, Germany, assignors toDeutsche Edelstahlwerke Alrtiengesellschaft, Krefeld, Germany Filed Nov.15, 1961, Ser. No. 152,659 Claims priority, application gserrnany, Nov.23, 196%,

9 Claims. (Q1. 26424) As known, difficulties arise in the production ofpressings for permanent magnets, especially if the magnet material isone based on barium ferrite. These are due to the extremely fine grainof the powder. The fineness of the powder prevents it from flowing,facilitates arching and in any event hinders it from entering the cavityof the die without manual help.

In order to overcome this drawback such powders have been submitted to aprevious process of granulation. However, this step also hasdisadvantages, firstly because it introduces an additional operation,and secondly because trouble arises if the granulated powder is to beused for the production of anisotropic permanent magnets and compactedin a directional magnetic field. A granulated product of such a kindcontains magnets oriented in random directions and the individualgranule is practically not affected by the directional magnetic field.Another known method is to press the powder when Wet. Wet processing isboth complicated and tedious. Moreover, special steps must be taken todeal with the volatile wetting agent.

It would therefore be very desirable if a method could be devised whichpermitted the powder to be fully automatically processed by pressingwithout wetting or granulating the same. One step in this direction hasbeen proposed of introducing the powder into the cavity of the diethrough a feeder and of energising an electrical coil which surroundsthe die cavity for the purpose of sucking the powder magnetically intothe same. This method has been successful in practice. However, fromtime to time the feeder (a filling shoe or box) requires recharging byhand by the operator attending the press, because the powder will not ofits own accord flow from a major storage container.

In order to perform the operation of refilling the feeder by automaticmeans the present invention proposes to magnetise the powder beforecharging it into the devices which feed it to the press and into thedie. Surprisingly it has been found that by magnetising the powder itbecomes flowable. Although it tends to cling lightly together, it doesnot form pronounced lumps and, although to the touch it feels like dampsand, it flows from the hopper of the press into the feeder and thenceinto the die cavity in a manner which is nearly ideal.

The fact that the powder can be made to flow in this Way may also beutilised on other occasions when it is desired to convey the powder fromone place to another.

The method can be carried out by apparatus as shown in the accompanyingdrawings in which:

FIGURE 1 is a sectional elevation of one embodiment; and

FIGURE 2 is a sectional elevation of another embodiment.

Referring to FIGURE 1, for magnetising the powder, the latter isconveniently introduced into the interior of a fairly large diameterair-cored coil 1 (field strength about 1500 gauss), the bottom of thecoil being closed by a sliding trap 2 during the process ofmagnetisation. The coil need be energised for only a short period at theend of which the magnetised powder charge can be drained by opening thetrap 2 to permit the powder to flow into a storage container 3, or thelike, for subsequent feeding into the hopper of the press.

Alternatively, see FIGURE 2, a storage container 20 affixed to the pressin a more elevated position may itself be surrounded by a magnetisingcoil 10 which is briefly energised to generate a field whenever a freshcharge is filled into the container. When the slide 30 is opened, thepowder, which is rendered fiowable by magnetisation, is released to fallthrough the pipe to the conventional filling shoe '50 and inconventional manner with the shoe brought over the cavity of the die 70,the magnetised powder is magnetically sucked into the cavity byenergising the coil 69.

What we claim is:

1. A method of producing pressings to form permanent magnets fromferromagnetic powders of such fineness as to be non-flowable whichcomprises the step of trapping the powder and magnetising the powder bythe brief application of a field thereto while so trapped so that theparticles cling lightly together and thereafter releasing the magnetisedpowder to flow solely by gravity into the cavity of a die and pressingit.

2. A method as in claim 1 wherein the trapped and magnetized powder isbased on barium ferrite.

3. A method of causing ferromagnetic powders, that are of such finenessas to be practically non-flowable by gravity, to flow invariably whenreleased to the influence of gravity, including the step of magnetizingsuch a fine powder by the brief application of a field thereto While itis trapped in a container from which it can be downwardly released untilits particles cling lightly together suffiicently for the magnetizedpowder to flow spontaneously under its own weight when released fromsaid container.

4. A method of transferring a ferromagnetic powder, of such fineness asto be practically non-fiowable by gravity, from one point downward toanother point including magnetizing the powder by the brief applicationof a field thereto while releasably held at said one point to impart toit the property of spontaneously flowing under the influence of its ownweight to said another point when released from said one point.

5. A method as in claim 4 wherein said powder includes barium ferrite.

References titted by the Examiner UNITED STATES PATENTS 2,742,185 4/57Landry. 2,959,823 11/60 Schwabe et al. 2,984,866 5/61 Schwabe. 2,984,8715/61 Venerus.

ROBERT F. WHITE, Primary Examiner.

WILLIAM J. STEPHENSON, ALEXANDER H. BROD- MERKEL, Examiners.

1. A METHOD OF PRODUCING PRESSINGS TO FORM PERMANENT MAGNETS FROMFERROMAGNETIC POWDERS OF SUCH FINENESS AS TO BE NON-FLOWABLE WHICHCOMPRISES THE STEP OF TRAPPING THE POWDER AND MAGNETISING THE POWDER BYTHE BRIEF APPLICATION OF A FIELD THERETO WHILE SO TRAPPED SO THAT THEPARTICLES CLING LIGHTLY TOGETHER AND THEREAFTER RELEASING THE MAGNETISEDPOWDER TO FLOW SOLELY BY GRAVITY INTO THE CAVITY OF A DIE AND PRESSINGIT.